The invention relates to a commercial system for lifting and supporting an object i.e. a corner of an automobile; particularly to a two part jacking system including an improved robust power unit that can be used to place and elevate an improved robust jack stand. The inventor of the present invention is a pioneer of the two part jacking system and holds numerous patents for two part jacking systems, some of which are described below.
Briefly, the commercial two part jacking system consists of a mobile power unit and a set of separate mechanical jack stands. Examples of the two part jacking system and mobile power unit are described in detail in Re. 32,715; U.S. Pat. Nos. 4,589,630 and 6,986,503. Some examples of the jack stands are described in detail in U.S. Pat. Nos. 4,553,727; 5,110,089; 5,183,235 and 5,379,974. The stands are capable of being vertically extended and retracted from the garage floor or road surface and, when extended, can be locked in place at a desired position by a ratchet and pawl assembly. The power unit has a wheeled mobile chassis adapted to carry a plurality of the jack stands, and has a pair of lift arms adapted to mate with the outermost jack stand for placement and removal.
In use, the commercial mobile power unit is operated from its handle. It is maneuvered under a vehicle to place a jack stand in a desired location for lifting and supporting the vehicle. The power unit is activated from the handle, and the jack stand is then extended vertically to the desired height, thus lifting the vehicle on the stand. By operating the controls at the end of the handle, the operator can cause the power unit to disengage from the stand, and the stand will remain locked in its extended supporting position under the vehicle.
After the stand is raised and locked in place supporting the vehicle, or other load, in an elevated position, the power unit lift arms are lowered and the power unit is disengaged from the stand and pulled away, leaving the stand in position supporting the load. Another jack stand, carried within the chassis, is automatically transferred to the forward end the chassis for placement at another desired location of the vehicle or for use in lifting and supporting another vehicle.
To lower the vehicle and remove the stand, the power unit is maneuvered to re-engage with the stand. The engagement causes any existing jack stands carried within the chassis to be automatically transferred rearward within the chassis. By manually operating a control at the end of the handle, the operator can cause the power unit to re-engage with the stand, and to disengage the ratchet locking mechanism of the stand, and to lower the stand to its original position. The power unit remains engaged with the stand and can be pulled away from the vehicle with the stand carried within the chassis.
The original commercial power units were adapted to carry up to four jack stands within the chassis. Additional jack stands could be acquired to reload the power unit, so that a single power unit could be utilized to efficiently place and actuate numerous jack stands. It was found that many commercial users would utilize all of their available jack stands, and the power unit was thereafter useless until another jack stand was available to be extracted and reused. The present inventor developed a slide forward bridge that adapted the power unit to function as a load-lifting jack to more fully utilize the power unit. This invention is illustrated in U.S. Pat. No. 6,779,780 entitled Lift Bridge For Use With a Power Unit and a Load Lifting Jack, along with several other patents related to additional features of the lifting system.
In the development of these lifting devices, several design challenges were presented that led to improved, innovative components and assembles of the present invention.
One such design challenge of the jack stand related to a lifting plate raised by the ends of a pair of lift arms on the power unit would sometime shift during lifting, and required redesign of these mating components so they would be self-aligning.
Another design challenge of the jack stand related to a locking mechanism that retained the second frame during elevation of the control frame was not reliable and had a short life, and required redesign with specific new cam angles, materials and heat treating specifications.
Another design challenge of the power unit related to the original hydraulic ram operating on the middle of the lift arms and required excessive and pivotal travel. A new design pushing directly on the rear of the lift arms, and retained within rugged retaining channels was developed.
Another design challenge was to improve the control features of the handle during use, and to improve the handle for movement of the power unit and for compact storage of the handle on the power unit for shipping and when the power unit was not in use.
Another design challenge was that a manual lift bridge should be provided for the basic power unit, stored at a first position on the power unit; and readily available to be placed at a second position on the forward ends of the lift arms, so that the basic power unit could also function as a load lifting jack.
Another design challenge related to the lift arms of the power unit having an extruded recessed channel in the upper surface for retaining a compression spring for advancing the automatic-slide-forward-bridge. The lift arms were difficult to manufacture, had a high scrap rate and were thus not robust to produce. Also, the slide-forward bridge was difficult to produce, was difficult to assemble, and was not as smooth in operation as desired. A new slide-forward bridge for the mobile commercial power unit needed to be developed.
Another design challenge resulted from the redesign of the retaining channels for the rearward ends of the lift arms. This led to the design of a new safety mechanism to lock the rear ends in position when the power unit was functioning as a load lifting jack.
In view of the foregoing design challenges, it is an object of the present invention to provide an improved commercial power unit having components that are robust to manufacture and assemble.
It is another object to provide an improved jack stand that has a self aligning lift plate.
It is another object to provide an improved jack stand with a reliable locking mechanism between the extendable frames.
It is another object to provide a power unit with improved controls for the jack stand.
It is another object to provide an improved handle for the power unit for control of the jack stand; and for positioning the handle for movement, shipment and storage of the power unit.
It is another object to provide a manual two-position bridge component that can be reliable and durable in use and can be stored on the power unit.
It is another object to provide and an automatic-slide-forward-bridge assembly having components that are robust to produce and assemble, and that are reliable and durable in use.
It is another object to provide an improved durable safety mechanism for a hydraulic jack and for the power unit when it is used with the bridge directly as a load lifting device.